Previous work has been done in the field of enclosed cell implantation or transplantation using Millipore chambers. These chambers were generally implanted in the peritoneal cavity.
The present invention involves use of a blood vessel as an implantation site in order to provide the closest proximity to plasma and to enhance diffusion by taking advantage of intravascular pressure. The material of which the chamber-forming device is made must be tolerated in a blood vessel without causing thrombosis and should permit the choice of various degrees of porosity. Expanded polytetrafluoroethylene (PTFE) fulfills both of these requirements.
The device may be implanted as a "button" in the wall of a blood vessel (artery or vein) in which case it would be subject to the pressure gradient between the blood vessel and tissue. The device may also be implanted between an artery and a vein to serve as a "sieve" between the two in an arteriovenous fistula. This latter approach has the advantages of a greater pressure differential across the chamber and of providing greater filtration surface area.
The foregoing and other objects of the invention will become apparent as the following description proceeds, especially when considered with the accompanying drawings.